Hi The hump sounds a lot like power supply noise.
Bob On Mar 22, 2013, at 7:43 PM, Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote: > The switcher loop compensation may cause peaking of reference or other noise > in this region. > Amplifier supply bypass networks together with coupling capacitors can cause > such peaking. > > Bruce > > Magnus Danielson wrote: >> Hi Bruce, >> >> Switcher, yes. But with a fair bit of filtering on it. See page 18 of >> http://www.thinksrs.com/downloads/PDFs/Manuals/FS730m.pdf >> >> Switcher to get +24 V, LC-filtering with two serial 1,28 kHz filters. >> Then an LDO (LM1086CS-ADJ) to drop it to +22 V which is actually used. >> >> 700 Hz and 2 kHz doesn't sound like modern switching rates. >> >> FLL/PLL? No. >> >> Cheers, >> Magnus >> >> On 03/22/2013 10:01 PM, Bruce Griffiths wrote: >>> Switch mode power supply ? >>> FLL or PLL loop? >>> >>> Bruce >>> >>> Magnus Danielson wrote: >>>> Fellow time-nuts, >>>> >>>> I got the oppertunity to measure a cesium with my TimePod, I hooked up >>>> on the FS 730/1 and noticed a bump in the phase-noise. I by-passed it >>>> and the bump was not there. Turns out that it had a 20 dB increased >>>> phase-noise at 700 Hz. So, we tried the other FS 730/1 they had, and >>>> it showed the same 20 dB increase, but at 2 kHz. It was not changing >>>> with load. There was a fair amount of 50 Hz and 150 Hz in the spectrum >>>> too. >>>> >>>> It was a fairly wideband rise of noise, rather than the spikes. >>>> >>>> I did look in the schematic, but did not have the time to measure >>>> inside them. >>>> >>>> Have people seen this before? A fair idea of what aspect in the design >>>> which is to blame? Let's learn from this, right? >>>> >>>> My ideas so far: >>>> >>>> The input has a low-Q LC filter, could it be the noise shaped as it >>>> goes into the input limiter, considering that the LC filter might be a >>>> little detuned from 10 MHz. >>>> >>>> Another theory would be a resonance in the power, but I have not found >>>> an obvious place in power design that would be a give-away. >>>> >>>> So, thoughts? Bob? Bruce? >>>> >>>> Cheers, >>>> Magnus >>>> _______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
